A known method for introducing hydroxyl groups into a cage silsesquioxane compound composed of eight silicon atoms (referred to as “T8-silsesquioxane compounds”, hereinafter) comprises of the following steps: synthesis of the triflate-group containing silsesquioxane by the addition of trifluoromethanesulfonic acid to T8-silsesquioxane containing eight intramolecular vinyl groups; and hydrolysis of said silsesquioxane in either acetone or dioxane in the presence of sodium carbonate (see, e.g., Patent Literature 1 and Nonpatent Literature 1).
However, approximately 85 to 90 percent of the resulting product prepared using the above-described method consists of trifluoromethansulfonic acid bound to only one vinyl group of each T8-silsesquioxane molecule, leaving a proportion of T8-silsesquioxane compounds unreacted. Therefore, the target compound must be isolated and purified from the mixture using techniques such as chromatography, resulting in a complicated process. In addition, the yield of the target compound tends to be low.
Patent Literature 1: U.S. Pat. No. 6,100,417.
Nonpatent Literature 1: Chemical Communications, 1289-(1999).